Surface acoustic wave (SAW) devices are used for many applications, such as radio frequency (RF) filters and duplexers. SAW devices combine low insertion loss with good rejection and can achieve broad bandwidths. SAW devices are typically very sensitive to temperature changes. The stiffness of a pyroelectric substrate material may decrease at higher temperatures, which may reduce acoustic velocities. Temperature-compensated SAW (TCSAW) devices have been developed. These TCSAW devices may include an overcoating of interdigital transducers (IDT) structures with layers that increase stiffness at higher temperatures. While these TCSAW devices desirably reduce temperature coefficient of frequency, they are also associated with various reliability challenges.
A pyroelectric effect may charge a substrate of the TCSAW device in proportion to a change in temperature. If the induced charge is of sufficient size, an electrostatic discharge event may occur damaging the TCSAW device.
IDTs of the TCSAW devices may include electrodes having a copper-dominant layer. Under a constant bias, the copper may oxidize, into copper cations, and may migrate through lithium niobate sites in the substrate. The copper cations may be sourced from the electrodes with positive potential and migrate toward the electrodes having negative potential.
The overcoating used to provide temperature compensation in TCSAW devices may be porous to humidity. Therefore, in some situations, the electrodes of the TCSAW devices may corrode due to presence of moisture in the devices.